1. Field of the Invention
The present invention relates generally to a video recording apparatus and a recording method therefor. More particularly, the invention relates to a video recording apparatus and a recording method therefor, in which compression of video data is performed by a software process.
2. Description of the Related Art
In general, when a personal computer having a video data compression processing function performs video data compression by a software process on CPU without employing a dedicated hardware, such as expansion board or the like, a performance of compression process for performing compression process of a video data taken by a video capture device in real time without delay significantly depends on a performance of the personal computer, particularly CPU. Therefore, when the performance of CPU is not satisfactorily high, it is possible that compression process without delay cannot be realized. In such case, drop out of frame (frame drop out) is caused in the compressed video data can be caused. As a result, number of frames in the compressed video data can be smaller than that of the captured video data. If such compressed video data is reproduced, the reproduction period becomes shorter than the actually captured video period.
One example of a method to certainly provide necessary number of frames in the compressed video data even upon occurrence of the frame drop out has been proposed in Japanese Unexamined Patent Publication No. Heisei 8(1996)-111847, for xe2x80x9cVideo Recording and Reproducing Methodxe2x80x9d.
In the above-identified publication, upon performing compression of the video data, a motion vector amount which is increased and decreased depending upon motion of video image per frame or per video information block is constantly monitored to make judgment for the condition of the video image on the basis of the motion vector amount immediately before recording the compressed data on a disk drive so that a frame, in which motion is small and difference with preceding and following frames is small is not recorded on the disk drive. Upon reproduction, the frame not recorded is supplemented with the frame preceding or following frame for reducing non-smooth feeling so as to permit long period recording with a limited capacity of the disk drive.
On the other hand, Japanese Unexamined Patent Publication No. 10-155134 discloses a video signal recording method, reproducing method and a video signal recording and reproducing apparatus. In the above-identified publication, the motion vector amount per each frame is monitored to make judgment of the status thereof to perform dropping of frame.
The conventional video recording systems are also directed how to efficiently record the video signal for a long period on the recording apparatus of limited capacity, such as disk drive or the like to perform dropping of frames. Therefore, in such conventional video recording system, frame drop out caused due to delay pf processing timing upon performing video data compression process on the software.
An object of the present invention is to provide a video recording apparatus and a method therefor which can produce a compressed video data to be reproduced in the same period (frame number) as a period (frame number) upon actual capturing irrespective of picture image or motion to be compressed, without depending upon performance of personal computer upon performing video compression process on a software.
According to the first aspect of the present invention, a video recording method comprises:
first step of measuring a compression process period per one group of frame data of a video signal taken by video capturing; and
second step of performing frame dropping process in next one group of frame data when said compression process period exceeds a predetermined value.
According to the second aspect of the present invention, a video recording method comprising:
first step of measuring a motion vector amount per one group of frame data of a video signal taken by video capturing; and
second step of performing frame dropping process in next one group of frame data when said motion vector amount exceeds a predetermined value.
According to the third aspect of the present invention, a video recording method comprises:
first step of measuring a compression process period and a motion vector amount per one group of frame data of a video signal taken by video capturing; and
second step of performing frame dropping process in next one group of frame data when at least one of said compression process period and said motion vector amount exceeds a predetermined value.
According to the fourth aspect of the present invention, a video recording apparatus comprises:
a video capturing portion taking a video data and outputting a first video signal;
a compression control portion receiving said first video signal, compressing said first video signal for outputting a compressed video signal;
a file output portion for writing and recording said compressed video signal;
said compression control portion including a timer measuring a compression process period and outputting a time information;
a motion detecting portion detecting a motion vector amount of said first video signal and outputting detected information;
a motion vector deriving portion deriving a motion vector amount per a group of frame data from said detected information and outputting a motion vector amount information;
a video compressing portion performing compression process for a second video signal output from said motion detecting portion and outputting said compressed video signal; and
a frame drop control portion making judgment whether dropping of frame is to be performed or not for a next one group of frame data from said time information and said motion vector amount information, and outputting a frame drop execution information to said motion detecting portion and said video compressing portion when judgment is made to perform dropping of frame.
In the preferred construction, the video capturing portion may comprise:
a capture control portion capturing control of said picture for outputting as video data; and
a capture data memory temporarily storing said video data and outputting said first video signal.
The file output portion may comprise:
a compression data memory storing said compressed video signal and outputting a compressed video data;
a file output control portion file controlling said compressed video data; and
a hard disk controlled by said file output control portion for storing said compressed video data.
If said time information does not exceed a predetermined period, judgment may be made that compression process for one group of frame data us completed, and said time information exceeds said predetermined period, frame drop process for next one group of frame data may be set.
A difference between a compression process period of said one group of frame data and a compression process period of the next one group of frame data, may be calculated and dropping of frame is determined by comparing the difference with a preset value.
If said motion vector amount information does not exceed a preset value, judgment may be made that compression process for said one group of frame data is completed, and when said motion vector amount information exceeds the preset value, dropping of frame for the next group of frame data is set.
A difference between a motion vector amount information of said one group of frame data and a motion vector amount information of the next one group of frame data, may be derived, and the difference is compared with a preset value for determining dropping of frame. In the alternative, a difference between a compression process period of said one group of frame data and a compression process period of the next one group of frame data, may be calculated and the difference is compared with a preset valued, when frame cannot be dropped in the next group of video data, dropping of the frame may not be performed in the next group of video data for repeat setting for frame dropping in two next group of frame data, and thereafter a post process is performed. A difference between a compression process period of said one group of frame data and a compression process period of the next one group of frame data, may be calculated and the difference is compared with a preset valued, when frame cannot be dropped in the next group of the frame data, dropping of the frames is brought forward to further next group of the frame data in the condition where the number of frames to be dropped is increased.
The second step may include determining of dropping of frame by deriving a difference between the compression processing period of said one group of the frame data and the compression processing period of the next group of the frame data and comparing the difference with the predetermined value when said compression process period exceeds said predetermined period.
The second step may include determining of dropping of frame by deriving a difference between the motion vector amount of said one group of the frame data and the motion vector amount of the next group of the frame data and comparing the difference with the predetermined value when said compression process period exceeds said predetermined period. In the alternative, the second step may include determining of dropping of frame by deriving a difference between the motion vector amount of said one group of the frame data and the motion vector amount of the next group of the frame data and comparing the difference with the predetermined value when said motion vector amount exceeds said predetermined period. The second step may also include determining of dropping of frame by deriving a difference between the compression processing period of said one group of the frame data and the compression processing period of the next group of the frame data and, if the next group of the frame data does not permit dropping of the frame, dropping of the frame being brought forward to the two next group of the frame data instead of performing dropping of frame in the next group of the frame data. The second step includes determining of dropping of frame by deriving a difference between the compression processing period of said one group of the frame data and the compression processing period of the next group of the frame data and, if the next group of the frame data does not permit dropping of the frame, dropping of the frame is brought forward to the further next group of the frame data in the condition where the number of frames to be dropped is increased.